Engine controller



Aug. 18, 1953 H. CARSON ETAL ENGINE CONTROLLER 3 sheets-sneetl FiledNov. 19, 1945 N5 mbk ATTORN En@` Aug. 18, 1953 cARsoN Erlu. l

ENGINE CONTROLLER Filed Nov. 19, A1945 3 Sheets-Sheet 2 Q Si M w N O o QG D mix i INVENTORS www? 7 NNN s sheets-sheet s ENGINE CONTROLLER /73/Ig /j H. CARSON ETAL n (a, w Z

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` ffy Aug. 18, 1953 Filed Nov. 19, 1945 Patented ug. i8, 149593 ENGINECONTROLLER Howard Carson and Clifford L. Muzzey, Dayton, Ohio, assignorsto General Motors Corporation, Detroit, Mich., a corporation of DelawareApplication November 19, 1945, Serial No. 629,578

11 claims. l

This invention relates to apparatus for controlling an airplane powerplant, for example, an internal combustion turbine engine driving apropeller.

An object of the invention is to provide manually controlled means forvarying the load on the engine in combination with a fuel governor whichautomatically controls the fuel supply so that a predetermined enginespeed will be maintained with varying load.

A further object is to provide engine temperature responsive means formodifying the manually effected control so as to reduce the loadautomatically to the extent necessary to prevent overheating the engine.

Another object is to provide for adjustment of propeller pitch either inthe positive range or in the negative range, to provide direct manualcontrol of blade angle during transition from the status of low torquein the positive range to the status of low power in the negative range,and to provide means for preventing shift of control from one range tothe other while the air speed of the airplane is excessive.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing, wherein a preferred embodiment of the present invention isclearly shown.

In the drawing:

Fig. 1 is a diagram of control apparatus embodying the presentinvention.

Fig. 2 is a chart showing the operation of the fuel governor.

Fig. 3 is a longitudinal sectional View in perspective, somewhatdiagrammatic, of a propeller hub and blade angle control unit with whichthe controller, shown in Fig. l, may be used.

Fig. 4 is a fragmentary sectional view on the line 4 4 of Fig. 3.

Fig. 5 is a fragmentary sectional view on line 5-5 of Fig. 4.

Fig. 6 is a fragmentary sectional view on line 5-8 of Fig. 4.

Fig. 7 is a fragmentary sectional view on line 'I-l of Fig. 4.

Fig. 8 is a fragmentary end View looking in the direction of arrow 8 inFig. '7.

The main control lever I in the cockpit is pivoted at I l and isconnected by link I2 with a plate i3 providing control cams, one ofwhich is designated by numeral I4. Cam I4 is engaged by roller I carriedby lever I6 connected with a piston rod Il of a piston I8 received by acylinder i9 forming a part of the fuel control servo 20. Cylinder I9 isconnected by passages 2| and 22 with ports 23 and 24 respectively of avalve guide 25 receiving a valve 26 having lands 21 and 28. Valve guide25 provides an inlet port 29. Valve 26 is under control by governorweights 36 and a spring 3| conned between valve 26 and lever I6. Thepressure of spring 3| is applied to valve 26 through a thrust bearing3|a. Piston rod I1 is connected with the fuel control apparatus notshown, but indicated by the scale 32. As power demand increases, thefuel rate is increased in order to maintain governed speed by upwardmovement of the servo piston I8. Weights 30 are pivotally supported by agear 30a driven by the engine and having a hub 30h supported by valveguide 25.

Referring to Fig. 2, the base line represents power output in percentageand the vertical line represents speed. The standard speedl for theturbine is represented by line N. As the piston rod Il moves up toincrease the fuel rate, the compression of spring 3| is relieved.Therefore the valve 26 is in equilibrium position at a speed whichdecreases as the fuel rate increases. This is represented by line N-P.The governor therefore has a droop characteristic which is conducive tostability. In order that the speed N will be maintained throughout therange of fuel adjustment, the cam I4 acts upon the roller l5 in a mannersuch that the spring 3| is defiected an amount equal to the amount thatit is relieved by upward movement of the piston rod I1. Therefore thegovernor speed will remain at value N throughout the range of fueladjustment. Theeffect of the cam |4 is to raise the droop line N-P tovarious positions such as N1-P1, Nz-Pz, Na-Pa. Therefore while thegovernor has a droop characteristic, the cam I4 operates to raise thedroop line so that the equilibrium position of valve 26 is always atspeed N.

Numeral 4|] designates generally the blade angle control servo. Thiscomprises a cylinder 4| receiving a piston 42 connected with a rod I43which operates, through connections not shown, a valve for controllingan hydraulic servo or torque unit which adjusts the blade pitch. Thefunction of the rod 43 is indicated by the pointer 44 and the scale 45.It will be noted that the adjustment ofv blade angle is between *30 andPipe 46 connects cylinder 4I with port 47 of a switch-over-valvedesignated generallyv by numeral 5U. Pipe 48 connects cylinder 4I withports 49 and 5|. There are two other ports 52 and 53 connectedrespectively with pipes 54 and 55. These ports are controlled by lands51 and 58 of a valve 56 having also guiding flanges 59 and 90, thelatter of which is engaged by a spring 6| which urges a roller 63(carried by valve 59) against plate |3. Valve 56 is in position forpositive pitch control. When main control lever yi9 is moved right intothe negative pitch control range, a cam 92 effects downward movement ofthe roller 93 and valve 55 to cause it to move into position to reversethe connections between pipes 54 and 55 and pipes 46 and 48 so that theunit il@ will be in condition for negative pitch control.

Pipes 54 and 55 are connected respectively with .el

ports 99 and 95 of a valve unit 19' having an inlet port 69 and drainports 9.1 and 98.. Inlet 99 is connected with an oil pressure sourcesuch as pump 53a and pressure control valve. VFlow from inlet 59 throughports 54 and 55 is controlled by lands 1| and 12 of a valve 13 providinga piston 1li under the control of oil pressure entering through a pipe 15 connected with a pressure pump 16 and connected with an hydraulictorque meter associated with the reduction gears connecting the turbinewith the propeller. The turbine shaft is indicated at 11 and thepropeller shaft, which is not shown, is represented by a circle or ring18. Ring 18 provides pivotal supports for planetary gears 19 meshingwith a ring or internal gear 8B and a gear 8| connected with turbineshaft 11. Ring gear 80 provides arms 82 connected with piston rods 83 ofpistons 84 received by cylinders 85 connected as shown with pump 19 andwith pipe 15. One of the cylinders B5 is provided with a relief port S9.As this torque meter is shown, direction of rotation of the turbineshaft and propeller shaft is counterclcckwise and the direction oftorque on the ring gear 8.9 is clockwise. As engine torque increases,there is an increase of oil pressure in cylinders 85 and therefore inthe cylinder 15 which receives the piston 14 of valve 13.

Oil pressure (varying with engine torque) acting upon piston 11| isopposed by the force of a spring 90 located between the land 1| and apad 9| carried by rod 92 connected with a piston 93 received by acylinder 99 connected by pipe 95 with a source of oil pressure such as apump 95a. Oil pressure above piston 93 urges rod 92 downwardly so that aroller 99 carried thereby is urged into engagement with a cam 91operated by lever I9. Movement of the lever l0 in either direction toincrease the power for positive or negative pitch causes cam 91 so to belocated that oil pressure will force the rod .92 down to increase thecompression of spring 90, thereby effectingan increase of blade anglecalling for increase in power output from the turbine to the propeller.As power output increases, there is an increase of pressure in cylinders85 of the torque meter and the pressure in cylinder 1d Yof the valveunit 19. Valve 13 comes rinto equilibrium position when the torque orpower output is equal to that demanded by the compression of spring 90which is controlled by cam 91.

Cam 91 is controlling so long as the pressure above the piston 93overcomes the pressure of spring 99. In order to protect the turbineblades against overheating, it is necessary to interpose meansresponsive to turbine exhaust temperare for lowering the oil pressure onpiston 93 to a value less than the force of spring 90 so thatthis-spring can be relieved to effect a reduction of engine power outputby effecting', through the unit 49, a. reduction in blade angle. Inorder to reduce pressure above piston 93, there is provided a reliefvalve |00 having a balanced valve |0| controlling a drain port |02 and aport |03 connected with pipe 95. A spring |04 is normally effective tourge valve |0| upwardly to block the port |02. To open the relief port|02, valve HH is moved downwardly by a lever |05 connected with rod 92and having a floating fulcrum provided by pins |06 and |01 carried bypiston rod |08 of a piston |09 movable in a cylinder I |9 normallybalanced in a non-eective position by theoil pressure on the lower sideand by a spring on the upper side. The lower end Vof cylinder H0 isconnected by pipe ||2 with a source of oil pressure having a reliefvalve, not shown, controlled by a thermostat located in the exhaust pipeof the turbine. This thermostat is one which is quickly responsive tovariations in exhaust gas temperature. `On a cold day, when the airentering the turbine is relatively cool, the temperature of the turbineblades may not exceed a safe value even for the highest power outputdemanded by cam 91. Under these con- -ditions the oil pressure on piston|09 will be such as to elevate the piston |09 to a position where thelever |05 will always be above the end. of valve |0| for all positionsrof 4the rod 92 asv determined by the cam 91.. On a hot day, the turbineblade temperaturev will be higher, and may exceed a safe limit when theturbine is putting out a certain amount of power to the propeller. Asthe temperature of the exhaust gas increases above a certain value, theoil pressure in cylinder I|0 decreases, thereby permitting the spring tomove piston |09 down into a position wherein the spring balances the oilpressure. The pins |06 and |01 are moved into a new location such thatwhen the cam 91 is moved in either direction from neutral or Zero torqueposition, downward movement of the rod 92 will effect, through lever|05, a downward Vmovement of valve |10! to connect pipe 95 with drain|02 sothat the pressure above piston 99 will be decreased to a valuesuch that the spring 9.0 is permitted to expand to move follower 95 awayfro-mcam91 and allow valve 13Ato move upwardly to connect port `|36 withport 69 whereby downward movement of the piston Z is-efected to decreasethe blade angle, thereby decreasing the power output of the-engine inorder to maintain the turbine blade temperature within safe limits. Theeifect of increase of exhaust gas temperature to certain high valuesamounts substantially to placing a ceiling on the amount of torque whichcan be demanded by the manual setting of cam 91.

Thus the control of blade angle is made responsive to demand for poweroutput as determined by the position of cam 91. However, the control bycam 91 is removed for the sake of `protectingthe turbine blades againstoverheating. The torque pressure balancing spring 90 is controlled bymeans responsive to turbine exhaust temperature when that temperatureexceeds a va-lue safe for turbine operation. While that temperature isbelow the safe value, the cam 99 has control of spring 90. When exhaustgas temperature reaches the danger point, the compression of spring -90is no longer controlled bycam 91, but by oil pressure above piston `93which varies approximately in accordance with Yexhaust gas temperaturewhen in a range near .the danger point.

The blade servo piston rod 43 carries a roller received by a rectangularopening |2|in plate I3 for positive pitch control or by a-rectangularopening |22 for negative pitch control. The openings |2| and |22 areconnected by a gate |23 which must receive the roller |20 during thetransition from positive to negative governed pitch. The inclination ofthe gate |23 is such as to maintain a predetermined schedule of bladeangle with respect to position of lever I0 during the shift betweenpositive and negative pitch positions. This is necessary since, at lowblade angle and power output, the ratio is zero or nearly equal to zero,Q being torque due to blade angle change and being blade angle. Thesurface |2|a of the opening |2| will be engaged by the roller |20 whilepositive blade angle is high. Therefore it is necessary that the airspeed of the plane be low in order to reduce positive blade angle to alow value before the shift from positive to negative pitch can be made.In like manner the surface |22a. of opening |22 makes it necessary thatthe air speed be low in order to reduce the negative blade angle to alow value before the shift can be made from negative to positive pitchcontrol.

The manner in which blade angle is controlled by the piston rod 43 willnow be described with reference to Figs. 3 to 8.

Fig. 3 shows, in perspective, a type of propeller hub equipped withblade angle control apparatus of the type shown in Blanchard and MacNeilpatents, No. 2,307,101 and 2,307,102, issued January 5, 1943. The engineshaft |30 extends from the engine frame |3| and supports and drives apropeller hub |32 providing blade receiving sockets |33, each providingbearings |34 for supporting a blade for rotation about the axis of itsroot |35. Each blade root |35 is connected with a torque unit cylinder|36 also connected with a plate |31 providing a bevel gear segment |30meshing with a master or equalizing bevel gear |39 supported by abearing |40 carried by the hub |32. Each cylinder |36 is closed at itsouter end by a cover or head |4| and at its inner end by a portion |42of the hub |32 which provides a bearing |43 concentric with bearings|34.` Cylinder |36 is provided with internal helical splines |44 matingwith external helical splines |45 of a piston |46 having internalhelical splines mating with external helical splines |41 provided by thehub portion |42. The construction is such that inward movement of thepistons |46 eiects blade angle increase in the direction of arrows |48and |49 while gear |41 rotates in the direction of arrow |50.

The hub |32 carries a plate |52 secured Vthereon by tubular nut |53(Fig. 5). Plate |52 carries a cover |54, thus providing an oil reservoirand an enclosure for a pump |92, a pressure control valve PC, anaccumulator control valve AV and a. distributor valve |10. There extendsinto this enclosure a non-rotatable sleeve |55 which is supportedconcentric with the shaft |30 by sealed bearings provided by the plate|52 and the cover |54 as shown in detail in the Blanchard and MacNeilpatents referred to. the bearings is shown at |56 in Fig. 5; and theseal for this bearing is marked |51. To prevent rotation of the sleeve|55, it is provided with a tang |50 received between two brackets |59attached to the engine frame .|3|. Thesleeve |55 l..

One of supports a ring gear |60 having an arm 6| with which the pistonrod 43 (Fig. 1) is connected in any suitable manner. Gear |60 drivespinions |62, each attached to a shaft |63 supported by the sleeve |55and providing a screw |64 threadedly engaging a grooved control ring |65receiving a shoe |66 which is caused to move parallel to the axis of theengine shaft |30 when the gear |60 is rotated by the piston rod 43.

Referring to Figs. 4, 5 and 6, the shoe |66 carries a pivot stud |61which connects the shoe with a bar |68 having a slot |69 receiving ashoe |1| pivotally supported by a carriage |12 forming part of adistributor valve unit |10 supported by the plate |52. The carriage |12carries on each side thereof a pair of trunnlon wheels |13, each pairbeing received by the groove of a channel bracket |14 secured to themain frame |15 of the unit |10, which frame is attached by screws |16 tothe plate |52. 'Ihe carriage |12 carries a roller |11 for engaging alever |18 pivotally supported at |19 by the head of a screw fastened tothe frame |15 by a nut |8|. Lever |18 provides a notch |32 receiving apin |33 attached to a valve |84 which slides in a valve guide |05provided by frame |15. Guide provides inlet ports |86 located betweenthe lands |01 and |80 of valve |84 which control respectively ports |89and |90, As shown diagrammatically in Fig. 3, inlet ports |86 areconnected by pipe |9| with a pump |92 operated by a gear |93 meshingwith a gear |94 non-rotatively supported by the sleeve |55. The ports|89 are connected by pipe |95 with the outer or pitchincreasing ends ofthe cylinders |36. The ports |60 are connected by pipe |96 with theinner or pitch-decreasing ends of the cylinders |36.

The right end (Fig. 6) of bar |68 provides a slot 200 which receives astud 20| extending from a nut member 202 carrying a ball 203 received byhelical groove 204 provided by a shaft 205 rotatable in a bearing 206provided by the plate |52. Shaft 205 is connected with a plate 201having an arcuate slot 208 through which there extends a screw 209passing through a plain hole in a coupling plate 2 l0 attached to ashaft 2| The plates 201 and 2| 0 provide for angular adjustment betweenthe shafts 205 and 2||, this adjustment being maintained by thetightening of a nut 2|2 on the screw 209. Shaft 2|| is supported in abearing 2| 3 provided by a plate 2|4 attached to the housing |32 andsupporting a bearing 2| 5 for an idle gear 2|1 which connects gear 2|6attached to shaft 2|| with gear 2|8 connected with master gear |39 (Fig.7). One end 220 of a spring 22| is vreceived by a notch in the bearing2|3; andthe other end 222 is received by a notch in the hub of plate 2|0attached to the shaft 2|| which spring 22| surrounds. The spring 22| isunder tensiony such that back lash of the gear train 2|6, 2|1 and 2|8 istaken up.

The operation of the mechanism is as follows: If the movement of thepiston rod 43 of Fig. 1 provides blade angle change from 30 to +90, ortotal, the mechanism shown in Figs. 4 to 8 provides for this amount ofblade angle change. Assuming that the piston rod 43 is in the 30position, the pivot stud |61 would be located as shown in Fig. 6; andthe nut member 202 would be located as shown in Fig. 7, thereby locatingthe stud 20| in the position shown in Fig. 6. The carriage 12 will belocated to the right of the position as shown in Figs. 3 and 5. Sincethe valve |84 is acted upon by centrifugal 'acre-,ici

-tion of arrow 43a. of Fig. 3, to eiect movement of the control ring.|65 toward the left as in Figs. 3 and 5 or up in Eig. 6,*thereby movingthe pivot stud |51 to a positionshown as |61' in Fig. 6. While .studremains fixed carriage i12 moves to |12 in Fig. 6 or toward the leftofits Iposition shown in Fig. 5, therebypermitting upward movement of thevalve |84 to connect ports |86 and |89, thereby admitting .pressurefluid to the upper ends of cylinders |36 which causes blade angle toincrease by turning of the blades in the directions of arrows |48 and.|49 in Fig. .3. Such rotation of the blades about the root axes is.accompanied by rotation of the gears |39 and -v 2 8 in the direction ofarrow |50 in Figs. 3 and 4., thereby causing counterclockwise rotationof shaft 205 as indicated by arrow 205e when viewed in the direction ofarrow 205D. VThis causes the nut 202 to travel downwardly in Fig. 1 andthe stud 20| to move downwardly in-Fig. 6 to a position shown at 20|',thereby restoring the carriage |12 to the full line position shown inFig. 6 or to the neutral position shown in Fig. 5. Therefore, when thedemanded blade angle change has been effected, further change isarrested by restoration of the valve |34 to neutral position. Positions|61 of stud |61 and 20| of stud 20| correspond to a yblade angleintermediate the extremes of the range from to +90". If full ieatheringor 90 blade angle has been required, the stud |61 would have been movedby the piston rod 4 3 to vaposition |51", the carriage |12 would havemoved to aposition above the position indicated at l't2; and this wouldhave effected a blade angle change resulting in a movement of the stud20| to aposition 20|, thereby restoring the carriage |12 to neutralposition by the time +90 blade angle had been obtained.

ln order to eiect complete feathering of the blades and also to effectthe unfeathering operation, a fluid pressure accumulator is provided.This accumulator comprises a cylinder :235 supported by the hub .i 32and having and inner head 23| and an outer head 232 between whichavpiston 233 is located. The space between the piston 233 and the head232 is lled with compressed gas through a check valve 234, thus drivingthe piston 233 toward the head 23|. During normal operation, the spacebetween the piston 233 and the head 23| receives oil pressure through apassage 235 which is connected with the pump- |92 by an accumulatorcontrol valve .AV and pipes 235 and 19|, the pressure in said pipesbeing controlled by a pressure control unit PC which comprises a Valverod 2li-chewing a dashpot head 24| received by a cylinder .242 connectedwith pipe 233 and urged outwardly bycentriiugal force acting in thedirection Aof arrow 2/i3yand by a spring 244 in opposition to fluidpressure acting upon the lower (in Fig. 3) surface ,of a .piston Valve245 received by a cylinderr24 and controlling a relief port241. Theinner end of cylinder 246 is connected by pipe248 with pipe |95. Valve245, being responsive to centrifugal force, causes the pressure in line|9| to increase as speed increases land this pressure is increased alsowhen cylinder 246 receivespressure from the pipe .|95

8 whichis under pressure. when there is a demand iur :pitch increase.

The .unit A'PC includes. also a minimum pressure control valve .providedby a rod .250 having lands 25| vand .252 4Jfior rcontrolling theconnection between l.port 241 .and a discharge port 253. The rod 250.has adashpot head 254 engaged by a `spring y255 klocated in a cylinder255 connected with lcylinder V2.412. The force of spring .255 is opposedby the fluid pressure acting upon the under -Cin Fig. 3) vside Aof valveland 125|. The pressure .available in pipe [al will be limited to aminimum value by .movementof rod 2.50 to a position for connecting theports 241 and 253', Valve 245 having opened port 241. Up to a certainrotative speed of the hub, the pressure is limited toa minimum value inorder that the accumulator -`willloe fully charged within ashort timeeven .while the engine is operating at .low speed. This minimum pressure.issuicient ior the pitch decreasing function ofthe torque units.

As lpropeller speed increases, valve 245, being under/control bycentrifugal force, requires greater lline pressure to causethe openingof the port @2.41. Therefore the pressure increases in pipe i9! labovethe minimi-1in `in order to make available, the rpressures required forthe Ipitch lincreasing `function which .requires greater p-ressure withincrease of speed.

While rod 250I of unit :PCis shown parallel with vrodzlil which is underthe .action of centrifugal force, it will be understood that lrod 250 isnot controlled by centrifugal force but is actuallylocatedat.rightanglesto rod 240. The units PC and AV are detailedlydescribed in the copending application of David A. Richardson, SerialNo. 613,563, .led August 30, yi945.

For the understanding of the present invention, itis suiiicient to statethat the accumulator control valve unit AV has a check valve 2150 whichnormally blocksflowirom the accumulator 230 to pipe .235. Whenfeatheringis required, ring .|65 is moved to the extreme left to cause aroller 26| (carried by a shoe 262 receivedin the groove of ring |55) toengage a cam 263 carried by a .lever Mend-to eiiectoutward movement ofsaid lever and of a rod .265,thereby opening the check valve 25,0.:Pressure oil then ,flows from the accumulator to underside (in Fig. 3)of a piston 268 thereby veiiecting the opening ofa valve 261 so that:the accumulator maydischarge to pipe 236 .through a by-pass around thecheck valve. During thisdischarge, vthe 4valve 251 is held open by cilpressure against the underside (in Fig. 3) Vof a piston268. Asfeatheringr is completed, the pressure diierential between the pressurein pipe 235 and the Ipressure against the .underside of piston 2,68decreases and spring 239 closes valve 261. Cam 263, having beenmomentarily contacted by vroller 20| during movement of ring |65 totheextreme left, check ValveZS- recloses. Therefore discharge of theaccumulator is prevented until it-is desired to/use accumulator pressureto assist in the unfeathering operation. This is effected vby right (inFig. 3) movement of ring |65 vwhicl'reifects momentary opening of checkvalve 260'; and theldischarge of the accumulator into pipes23and |9|takes place.

While the embodiment ofthe present inventionas hereindisclosed,constitutes a preferred form, it is to be understood .that other formsmightbeadopted, all coming withinthe scope ofthe claimswhich follow.

What is claimedis asiollows:

1. Control -apparatus vfor an enginefpropeller combination, thepropeller having blades rotatable about their longitudinal axes to varythe pitch position thereof comprising, manually controlled means forvarying the load on the engine including a fluid pressure operateddevice for varying the pitch position of Said blades, a manuallyoperable member for modifying the operation of said device, and meanscontrolled by the engine torque transmitted to said propeller and bysaid member including a source of fluid pressure and a valve forcontrolling flow from said source to said device, to control the pitchposition of said blades; a speed responsive fuel governor forcontrolling the supply of fuel to the engine to maintain a desiredspeed; and means including an abutment operable by said manual means andresponsive to engine temperature for modifying the effect of said memberupon the control means for said pitch varying device independently ofthe setting of said member in order to reduce the pitch position of saidblades so that overheating of the engine will be prevented.

2. Control apparatus for an engine-propeller combination, the propellerhaving blades rotatable about their longitudinal axes to vary the pitchposition thereof comprising, a device for varying the pitch position ofsaid blades including a spring, means responsive to changes in enginetorque transmitted to the propeller, an element for controlling thepitch varying device, said element being controlled by the spring andthe torque responsive means, and manually controlled means for varyingthe force of said spring; a speed responsive fuel governor including afluid motor and a control valve for controlling the supply of fuel tothe engine to maintain a desired speed; and means responsive to enginetemperature including a fluid motor and a relief valve opened ontemperature rise for modifying the manually effected control of theforce of said spring in order to prevent overheating of the engine byelfecting .a reduction in the blade pitch position.

3. Engine control apparatus having an engine-propeller combinationsubject to combined fuel rate and blade pitch changes for eiiicientpower development, comprising in combination, a fuel control servo foraltering the rate of fuel delivery to the engine including a speedresponsive device for effecting change of fuel rate delivery, resilientmeans opposing the speed responsive means and a oating lever operable bysaid fuel control for ilexing variably the resilient means and foreffecting a droop characteristie in the response of said fuel controlservo, .l.

a fluid servo for changing the blade pitch within a selected range ofadjustment, means for selecting a positive or negative range of pitchacljustment for the propeller blades, and means operable coincident withselection of a different range of pitch for the blades to also shift thedroop characteristic of said fuel control servo.

4. Engine control apparatus having an engine-propeller combinationsubject to combined fuel rate and blade pitch changes for eicient powerdevelopment, comprising in combination, a fuel control servo including agovernor valve with a variably stressed spring and lever support and afeed-back to the lever from said fuel control servo providing droopcharacteristics for increasing the fuel rate as the power demandincreases to maintain governed speed, said valve reaching equilibrium ata speed which decreases as the fuel rate increases, a blade angle servoincluding a pressure actuated piston and a control valve for matchingthe blade pitch to the power development of the engine, means responsiveto a change in torque of the engine for shifting the blade pitch in anincreasing direction to satisfy the power available, means responsive totemperature of engine operation for opposing the shift of blade pitch bythe torque responsive means, and manual means including a cam actuatingsaid lever support for coincidentally shifting the droop characteristicsof the fuel control servo, the range of blade angle change and theopposition to :the engine torque effected blade change.

5. Engine controlgapparatus having an engine-propeller combinationsubject to combined fuel rate andblade pitch changes for efficient powerdevelopment, comprising in combination, a fuel control servo foraltering the rate of fuel delivery tothe engine including a speedresponsive valve reaching equilibrium at a speed which decreases as thefuel rate increases, and a blade angle vservo operable to shift theblade pitch to absorb the power output of the engine in all equilibriumpositions ofA the speed responsive valve, said blade angle servoincluding a fluid pressure piston and cylinder adapted to effect shiftof the propeller blades, a source of fluid pressure for the piston andcylinder, ya. control valve for applying the fluid pressure to the saidcylinder, a switch-over valve for selecting the positive or negativerange within which said piston and cylinder will effect shift of theblade pitch, means responding to the torque of the engine transmitted tothe propeller for actuating the control valve, a resilient Iabutmentopposing movement of said control valve in responding to the inuence ofsaid engine torque, and means for altering the opposition offered by theresilient abutment to limit increasing blade angle shift to a safe valuefor the power output of the engine.

6. The combination set forth in claim 5 wherein the means for alteringthe resilient opposition includes a cam surface and follower with meansfor actuating the follower in response to engine temperature change.

7. The combination set forth in claim 5 wherein the means for alteringthe resilient opposition includes a cam surface and follower with meansfor actuating the follower in response to engine temperature change,manual means for shifting the cam surface to permit increase of controlvalve opposition for increasing blade angle change in either thepositive or negative pitch range, and means associated with said manualmeans for selecting the range within which said blades shall operate andfor limiting the extent of said positive and negative range.

8. The combination set forth in claim 5 wherein the means for alteringthe resilient opposition includes a cam surface and follower with meansfor actuating the follower in response to engine temperature change,manual means for shifting the cam surface to permit increase of controlvalve opposition for increasing blade angle change in either thepositive or negative pitch range, and means associated with said manualmeans for selecting the range within which said bla-des shall operateand for limiting the extent of said positive and negative range, andmeans actuated by said manual means for increasing the speed level atwhich the speed responsive means reaches equilibrium as the rate of fuelfeed is increased.

9. The combination set forth in claim 5 whereinthey means for alteringthe opposition to control valve movement includesA a mannaliy actuatedcam, a cam follower engageable'vvith the cam surface, a fluid pistonand'chamber operablev to move the follower against'the cam, a source ofuid pressure for the chamber and temperature responsive means operableupon engine temperature rise to reduce' the pressure .in said chamberand therebyl reduce tne opposition to movement of the control valve bythe engine torque conditions.

10. In an engine-propeller combination-a blade angle servo mechanism forshifting the blade angle in accordance with power demands for the engineto run at' constant speed, said servo'mechanism including a piston andcylinder, for controlling the pitch position of the blade, a source ofduid pressure and` a valve for controlling the application of pressurefluid to saidcylinden said valve having an equilibrium positionWherethere is no pressure application to the piston and cylinder, meansresponsive to engine torque applied tov the propeller Yfor effectingmovement of the valve in one direction avvay from the equilibriumposition, resilient means opposing movement of said valve by said torqueresponsive meansA away from the equilibrium position and capable ofeffecting valve movement in the oppositeA direction, manually operatedmeansf'or establishing a maximum of opposition to movement of said valveby said torque responsive means away from the equilibrium position forany blade pitch position, uid pressure means tending tdmaintain themaximum opposition establisiied'by the' manual means, and meansresponding to the temperature of said engine for modifying the pressuremain-- taining the maximum `opposition so that the control valve can bemoved from the equilibrium position on temperature increase of theengine.

11. Control apparatus for an'engine-propeller combination, the propellerhaving blades rotatable about their longitudinal axes' to vary the pitchposition thereof, comprising, a speed responsive fuel governor forcontrolling the sup-v ply of fluid to the engine to maintain a selectedspeed, a source of fluid pressure, a fluid pressure operated device forvarying the pitch position of said propeller blades, valve meansoperatively connected with said source and said device and operable tocontrol said pitch varying device so as to increase, reduce, or maintainthe pitch position of said blades, means responsive to the torque ofsaid propeller, first uid motor means operatively associated With saidvalve means and controlled by said torque responsive means forcontrolling the operation of said valve means, resilient meansassociated with said valve means and exerting a force in opposition tosaid first motor means, manually operable means for modifying the forceexerted by said resilient means, and.y means responsive to enginetemperature including second fluid motor means operatively associatedwith said resilient means for modifying the force exerted by theresilient means.

HOWARD CARSON. CLIFFORD L. MUZZEY.

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